Method of manufacturing pickup tubes



Tal-f July 27, 1965 R. L. vAN AssELr ETAL 3,195,515

METHOD OF MANUFACTURING PICKUP TUBES Filed Jan. so, 11962 'T INVENToRs /Faf l. IKM/455i 5 By W/z MM /l/. KVA/145K A7' rar/Vir www y United States Patent O 3,196,515 METHOD F MANUFACTURING PECKUP TUBES Robert L. Jan Asselt and William M. Kramer, Lancaster,

Pa., assignors to Radio Corporation of America, a corporation of Delaware Filed llau. 30, 1962, Ser. No. 169,840 7 Claims. (6l. 29--25.18)

This invention relates to television pickup or camera tubes. In particular, this invention relates to a novel method of manufacturing an improved target structure for television pickup tubes.

In the prior art, there are several commercially available tube type-s known as image orthicons. The image orthicon tube generally comprises an envelope having an electron gun in one end thereof. In the opposite end of the envelope is a photocathode. Between the electron gun and the photocathode is at least one mesh screen and a semiconducting storage target electrode.

During operation of the image orthicon tube, an image of a scene to be reproduced is directed onto the photocathode which produces photoelectron emission which in turn provides .a charge pattern on one side of the target electrode. The electron b-eam scans the opposite side of the storage target to read off the charge pattern thereon and'produces electrical output signals corresponding to the original input scene.

In the prior art, the storage targets for the image orthicon type of tube have been made of a thin membrane of glass, or of thin semiconducting materials, or of insulating materials with electrically conducting plugs therein. This invention is particularly related to storage targets of the semiconducting type. The semiconducting type storage target generally comprises an annular support ring having :a thin membrane of magnesium oxide or aluminum oxide, either of which may include certain impurities, supported across the aperture in the support ring.

A storage target of the magnesium oxide type is diicult to prod-nce. One of the reasons for this diiiculty is that the magnesium oxide must be stretched quite taut, across the support ring, to prevent target vibrations. If any mechanical vibrations occur during tube operation these vibrations will produce spurious signals in the output of the tube.

` with this invention by depositing on a suitable -support ring a supporting iilm of organic material; then metallic magnesium is deposited; and then the organic lm is removed just prior to oxidizing the magnesium.

The invention will be more clearly understood by reference to the accompanying single sheet of drawings wherein:

FIG. 1 is a partial sectional view of an image orthicon made in accordance with this invention;

FIG. 2 is an annular sectional View of a storage target in the process of being made, in accordance with the invention; and,

FG. 3 is -an annular sectional view of a completed storage type target in accordance with this invention.

arrests! Patented July 27, 1365v ICC Referring now to FIG. 1, there is shown an image orthicon tube 10. The tube 10 comprises an evacuated envelope 12 having an electron gun (not shown) positioned in the stem end thereof (to the left as viewed in FIG. l). Positioned on the inner surface of the face plate, in the opposite end of the envelope, is a photocathode 16. The photocathode may be of :any conventional materials, examples of which are the S-10 photosurface described in U.S. Patent No. 2,682,479 issued t0 Johnson, or the mult-alkali photosurface described in U.S. Patent No. 2,770,561 issued to Sommer.

In the envelope 12, spaced from the photocathode 16 toward the electron gun, is a tine mesh screen 17 and Ia semiconducting type storage target 18. The storage target 18 comprises an annular metallic support member 20 having a thin lm of oxidized metal, e.g. magnesium oxide thereon.

During operation of the image orthicon 10, light from a scene to be reproduced is directed through the transparent face plate onto the photocathode 16 producing a photo-electron image corresponding to the light from the scene. The photo-electron image is focused, and accelerated, by known techniques e.g. by use of the mesh screen 17, and lands on one side of the storage target 18 to provide a charge pattern thereon. An electron beam from the electron gun scans the opposite side of the storage target 18 to remove the charge pattern therefrom. The electron beam is reilected back toward the electron gun where it is fed into a conventional electron multiplier which produce-s electrical output signals from the tube. The output signals correspond to the light from the scene to be reproduced.

In order to manufacture a storage target 18, shown more clearly in FIG. 2, a thin lm of -organic material 24 is rst deposited onto and across an apertured support member or metallic support ring 20 before one deposits the magnesium metal. The thin organic lm 24 may be any of several known materials. Examples of materials which have been found suitable are collodion, nitrocellulose, or isobutyl-rnethacrylate. The organic iilm 24 functions as a temporary substrate for metal layer 22. Onto the organic lm 24 there is deposited by any suitable means, for example evaporation in a good vacuum, a film or metal 22 which is to be oxidized. The metal film may be a material such as magnesium and may be approximately 500 to 1,000 angstrom units thick.

In the prior ar-t, the oxidation of the metal lm and the removal of the organic substrate 24 were accomplished by baking the target structure 18 in an oven (not shown) having an oxidizing atmosphere. It has been found that, when this prior art method was utilized, the resulting magnesium oxide membrane was not stretched as tautly as desired across the support ring 20. One of the reasons for this condition is that .the support ring is normally made of molybdenum, which has a coefficient of thermal expansion or' approximately 5x10-6; the organic lilm 'is normally made of collodi-on, which has a coefficient of thermal expansion of `approximately )(10-6; while magnesium metal has a coeicient of thermal expansion of approximately 25 l06. Observations of the structure during the baking period reveal that, as the temperature of the oven and therefore the target subassem-bly is initially increased, the magnesium lm remains substantially flat even though both the magnesium and the organic substrate have a higher coefficient of thermal expansion than the support ring 20. It is assumed that gradual decomposition of the support substrate 24 causes it to shrink. Apparently, the organic lm 24 has little sheer strength and the magnesium ilm expands -freely along the surface of the organic layer. When a temperature in the oxidizing atmosphere of the prior art is obtained at which the organic material is removed, e.g. ap-

. D proximately 200 C., ythe magnesium film is deposited onto, or vbecomes supported directly by, thev metal support ring 20. Any further temperature increase causes the magnesium film -to wrinkle because the magnesium is expanding faster than the ring 20. The amount of wrinklling increases until oxidation temperature of the magnef sium is attained, approximately 400 C., and the kmagnesiumfilm is ychanged into magnesium oxide. Some tighgy ning of the film is observed during the'oxidationfprocess. However, this tightning can compensate for only a small amount of the looseness that develops Vin 4the magnesium film prior to oxidation. Therefore', it is extremely important that the magnesium film be deposited as a flat 'film on the support ring at a temperature close to the oxidation temperature of the magnesium. 'When -this is done, the magnesium film loosen-s very little before oxidation and is stretched tight lby the oxidation proces-S. Y

to a temperature not greater than the oxidizing tempera- Vtureof said metal, changing said atmosphere to an oxidizing atmosphere, and raising the temperature of said elements toa temperature above the oxidizing temperature v of said metal.

.'SfThe method of vmanufacturing a target electrode structure for use in a television pickup tube, said target l structurecomprising a thin membrane of oxidized material supported upon'an apertured support member, said method comprising depositing a .temporary support means across the aperturefin Ysaid apertured'support member,

, depositing the material to be oxidized onto said temporary` support means, providing an inert atmospherearound the elements including said support member, said temporary In accordance wi-th this invention 'it has ,been 'found' 'Y that when an inert gas atmosphere is utilized, examples f of which are helium and a rgon,rduring the initial temperature increase, this inert atmosphere prevents oxidation of the organic, or support substrate, 24 and permits the substrate to function as a support for the magnesium metal layer upto the oxidation temperature of the'magnelsium. In practice it has been found preferable'to switch the atmosphere in the oven to an oxidizing atmosphere Vjust below the oxidation temperature of the 'mag-nesium VsupportV means andlsaid.material'tobe oxidized, rai-sing the-temperatureof said elements to a temperature of approximately 325 C. while said elements are in saidinert atmosphere", changing said atmosphere to oxygen while within the temperature range ofi approximately 325 C.'

toapproximately 400 C., andfraising the' temperature of ,y said elements:to a temperature above theoxid-izing temto insure complete removal of the. organic substrate priorA Y tothe oxidation of the magnesium.

It has been found that taut targets of magnesium oxide 26 are provided when the inert atmosphere is changedto an oxygen'atmospher-e within the range of temperatures of about 325v C.A to about 400 C. VWithin this range aY temperature of approximately 340 C. is preferable.

`When practicing this invention ithasbeen found that,V

perature of said material to be oxidized.

4. The method of manufacturing atarget electrode of the type comprising a support ring Whichsupports afilm ofY oxidized material, said method comprising the steps of depositing Van organ-ic temporary support member on said'support ring, said support member `oxidizes if sub- 'jected to a temperature above 200,C.. in anoxidizing atmosphere, depositing a material'tobe oxidizedronsaid organic temporary support member, raising the temperav rture'of said'elements including said support ring, said at about 200 C. while still'in the. inert atmosphere, a black or dark brown color appears on the ring 2d :side of the aluminum 22. This deposit is probably a partial decom` position of the organic film 24. .l

Thus, the conventional-support ring with a conven-l tion-al organic film 24 thereon anda conventional layer of magnesium metal 22 may be manufactured into a quite` taut target electrode by raising the temperature in, the v oxidizing furnace while the furnace is filled Withv'an inert atmosphere., yWhen thertemperature is just below that at which the magnesium oxidizes (400 C.), the inert' atmosphere is'exhausted and the furnace-'is filled with organic temporary support member and saidmaterial to beoxidizedto 'ai temperature of about 325 C. while subjecting said elements to an inert atmosphere ,and subjecting said elements to an oxidizing atmosphere while raising said ,temperature fromabout 325 C. .to about 400 C.

The method of manufacturing a target electrode of Y v the typecomprising a film'of magnesium.ox-idesupported tautlyiacross the aperture in a .molybdenumV support ring, said method comprisingv the steps of depositing an organic. film on said support ring, said organic film beingdecom-V l posableA at a .temperature of about 200C. in an oxygenl atmosphere, 'depositing magnesium metal on said Vorganic oxygen so that the 'support substrate oxidizes and is re nesium oxide target as shown in FIG. 3.

What is claimed is: 1. The method of manufacturingV a'target electrode moved and the "magnesium drops onto the Vsupportring and is oxidized, giving artaut, physicallykstrong r'nag-VVV 50 assembly'for use ina television pickup tube, said method comprisingVfor-ming a subassembly, sad'subassembly in'- cluding an apertured support member having a temporary supporting film thereon andV a layer of metal on said sup' g film, raising the temperature of theele'ments including said supportring, said organic film and saidV magnesium metal to a temperature of approximately 325 C. while said elements arein an inert: atmosphere, raising'the temperature of said elementsthrough the range of approximately 325v C'.l to approximately 400 C., subjecting said ele` ments texan-.oxidizing atmosphere 'at'. a predetermined Vtemperature within Ysaid range,'and Vraising .the temperature above saidrangeto oxidize :said magnesium metal.

w 6.7 The method of manufacturing a 4target electrode as in claim 5 wherein said predetermined temperature is ap-` proximately 340 C. v Y Y Y y 7. The method ofmanufacturing an assembly compris-k ing the steps of depositing an organic material onto a por-ting film, saidrme'thod comprising? raising the tempera-` f ture of said subassembly to a temperature belowthe oxidizing temperature of said metal whilelsaid subassembly is ina non-oxidizing atmosphere, changing to an oxidizing atmosphere, and then raising theV temperature of saidVVV subassembly to a temperature above the oxidizing temy perature of said metal.

2. The method Vof manufacturing a target electrode f structure of the type comprising a film of oxidized metal stretched taut across an apertured support member, vsaid method comprising the steps of providing ya Vtemporaryorganic support film on saidapertured support member, p-roviding a layer of metal to vbe oxidized on said support film, providing yan inert atmosphere' around the elements v including said support member, said organic support film and said metal,.raising thetemperatureof said elements supportmember, depositing a ray sensitive means onto said organic material, raising the' temperature-ofA the elements v vrecited to a temperature above thatwhichwould destroy` nrcHARD H. EANES, JR., Primary Examiner.

''LaoN PEAR,Examiner. 

1. THE METHOD OF MANUFACTURING A TARGET ELECTRODE ASSEMBLY FOR USE IN A TELEVISION PICKUP TUBE, SAID METHOD COMPRISING FORMING A SUBASSEMBLY, SAID SUBASSEMBLY INCLUDING AN APERTURED SUPPORT MEMBER HAVING A TEMPORARY SUPPORTING FILM THEREON AND A LAYER OF METAL ON SAID SUPPORTING FILM, SAID METHOD COMPRISING RAISING THE TEMPERATURE OF SAID SUBASSEMBLY TO A TEMPERATURE BELOW THE OXIDIZING TEMPERATURE OF SAID METAL WHILE SAID SUBASSEMBLY IS IN A NON-OXIDIZING ATMOSPHERE, CHANGING TO AN OXIDIZING ATMOSPHERE, AND THEN RAISING THE TEMPERATURE OF SAID SUBASSEMBLY TO A TEMPERATURE ABOVE THE OXIDIZING TEMPERATURE OF SAID METAL. 